The immune system serves a vital role in protecting the body against infectious agents. It is well established, however, that a number of disease states and/or disorders are a result of either abnormal or undesirable activation of immune responses. Common examples include graft versus host disease (GVHD), graft rejection, inflammation, and autoimmune linked diseases such as multiple sclerosis (MS), systemic lupus erythematosus (SLE), and certain forms of arthritis.
In general, an immune response is activated as a result of either tissue injury or infection. Both cases involve the recruitment and activation of a number of immune system effector cells (i.e. B- and T-lymphocytes, macrophages, eosinophils, neutrophils) in a process coordinated through a series of complex cell-cell interactions. A typical scenario by which an immune response is mounted against a foreign protein is as follows: Foreign proteins captured by antigen presenting cells (APC's) such as macrophages or dendritic cells are processed and displayed on the cell surface of the APC. Circulating T-helper cells which express an immunoglobulin that recognizes (i.e. binds) the displayed antigen undergo activation by the APC. These activated T-helpers in turn activate appropriate B-cell clones to proliferate and differentiate into plasma cells that produce and secrete humoral antibodies targeted against the foreign antigen. The secreted humoral antibodies are free to circulate and bind to any cells expressing the foreign protein on their cell surface, in effect marking the cell for destruction by other immune effector cells. In each of the stages described above, direct cell-cell contact between the involved cell types is required in order for activation to occur [Gruss et al., Leuk. Lymphoma, 24, 393 (1997)]. In recent years, a number of cell surface receptors that mediate these cell-cell contact dependent activation events have been identified. Among these cell surface receptors is CD40 and its physiological ligand, CD40 Ligand (CD40L).
CD40 was first characterized as a receptor expressed on B-lymphocytes. It was later found that engagement of B-cell CD40 with CD40L expressed on activated T-cells is essential for T-cell dependent B-cell activation (i.e. proliferation, immunoglobulin secretion, and class switching. It was subsequently revealed that functional CD40 is expressed on a variety of cell types other than B-cells, including macrophages, dendritic cells, thymic epithelial cells, Langerhans cells, and endothelial cells. These studies have led to the current belief that CD40 plays a broad role in immune regulation by mediating interactions of T-cells with B-cells as well as other cell types. In support of this notion, it has been shown that stimulation of CD40 in macrophages and dendritic results is required for T-cell activation during antigen presentation [Gruss et al., Leuk. Lymphoma, 24, 393 (1997)]. Recent evidence points to a role for CD40 in tissue inflammation as well. Production of the inflammatory mediators IL-12 and nitric oxide by macrophages have been shown to be CD40 dependent [Buhlmann and Noelle, J. Clin. Immunol., 16, 83 (1996)]. In endothelial cells, stimulation of CD40 by CD40L has been found to induce surface expression of E-selectin, ICAM-1, and VCAM-1, promoting adhesion of leukocytes to sites of inflammation [Buhlmann and Noelle, J. Clin. Immunol., 16, 83 (1996); Gruss et al., Leuk. Lymphoma, 24, 393 (1997)]. Finally, a number of reports have documented overexpression of CD40 in epithelial and hematopoietic tumors as well as tumor infiltrating endothelial cells, indicating that CD40 may play a role in tumor growth and/or angiogenesis as well [Gruss et al., Leuk. Lymphoma, 24, 393 (1997); Kluth et al., Cancer Res., 57, 891 (1997)].
Due to the pivotal role that CD40 plays in humoral immunity, the potential exists that therapeutic strategies aimed at downregulating CD40 may provide a novel class of agents useful in treating a number of immune associated disorders, including but not limited to graft-versus-host disease (GVHD), graft rejection, and autoimmune diseases such as multiple sclerosis (MS), systemic lupus erythematosus (SLE), and certain forms of arthritis. Inhibition of CD40 may also prove useful as an anti-inflammatory compound, and could therefore be useful as treatment for a variety of inflammatory and allergic conditions such as asthma, rheumatoid arthritis, allograft rejections, inflammatory bowel disease, various dermatological conditions, and psoriasis. Finally, as more is learned of the association between CD40 overexpression and tumor growth, inhibitors of CD40 may prove useful as anti-tumor agents and inhibitors of other hyperproliferative conditions as well.
Currently, there are no known therapeutic agents which effectively inhibit the synthesis of CD40. To date, strategies aimed at inhibiting CD40 function have involved the use of a variety of agents that disrupt CD40/CD40L binding. These include monoclonal antibodies directed against either CD40 or CD40L, soluble forms of CD40, and synthetic peptides derived from a second CD40 binding protein, A20. The use of neutralizing antibodies against CD40 and/or CD40L in animal models has provided evidence that inhibition of CD40 stimulation would have therapeutic benefit for GVHD, allograft rejection, rheumatoid arthritis, SLE, MS, and B-cell lymphoma [Buhlmann and Noelle, J. Clin. Immunol, 16, 83 (1996)]. However, due to the expense, short half-life and bioavailability problems associated with the use of large proteins as therapeutic agents, there is a long-felt need for additional agents capable of effectively inhibiting CD40 function. Antisense oligonucleotides avoid many of the pitfalls of current agents used to block CD40/CD40L interactions and may therefore prove to be uniquely useful in a number of therapeutic, diagnostic and research applications.